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SVO: over head cam

List members

When Changing the camshaft you should always check clearances, and not just
the retainer to guide clearance.  Why you may ask..  If you are not the
original owner of the car, you usually don't know the complete history of
maintenance.  The OHC set-up is very reliant on the correct geometry being
maintained.  There are two ways to correct the geometry: 1. use longer
lifters (Melling sells them) and 2. Use longer valves. Depending on how
small the base circle of the cam is you might need to do both longer valves
and longer lifters.     You can use stock lifters with shims under them,
and/ or stock valves with lash caps.  

Most of the high lift cams use a much smaller base circle.  The reason for
this, is that the lobes have to go through the cam bearings, when being
installed.  If the same (stock) base circle is retained the lobes would be
to large to fit through the bearing. 

When a head is rebuilt by a high volume reman. shop.  They will most likey
have the stock cam reground to factory specs, by reducing the base circle. 
To compensate, they use longer lifters.  If you did not know there were
longer lifters and tried to simpley (BOLT IN) a new cam the geometry would
be wrong.  

The moral of this ramble.  Always check clearances